Reclaimed rubber



Patented Oct. 1, 1929 1,729,?i}?

f UNITED STATESPATENT OFF-ICE CHARLES H. CAMPBELL, F PITTSBURGH, PENNSYL'VANIA, ASSIGNOR TO AMERICAN GLUE COMPANY, OF BOSTON,MASSACHUSETTS, A CORPORATION OF MASSACHU- SETTS RECLAIMED RUBBER NoDrawing. Continuation of application Serial No. 124,107, fil uly 21,1926. This application filed November 22, 1928. Serial No. 321,280.

The invention relates to an improvement in further disadvantage whichresults from the reclaimed rubber, being the product obtained use of oilas a plasticizin g agent is that the from rubber that has once beenVulcanized oil will. have a softening effect on the rubber and afterwarddevulcanized. after it is revulcanized, when in contact with The presentapplication is a continuation heated surfaces such as pavements orroadof my prior co-pending application Serial ways. In the case ofrubber tires or rubber N 124 107 fil d J l 21 1926 heels this causes amaterial reduction in the The general object of the invention is to ladcarrymg property of the rubber, resultobtain an improved reclaimedrubber which 111;: In excessive distortion and wear.

. 10 before revulcanization possesses highly cfli- It is accordinglywithin the object of my cient workable properties without the use oflnventlon as pointed out to obviate these oil or with a quantity of oilmuch smaller llillCtlltlGS arising from the use of oil as :1 than isordinarily employed, and which re- SOitemng or plasticizing agent.claimed rubber after revulcanization gives a I have found that theobjects of my inresulting rubber much firmer in character, vention areattained if the reclaimed rubber 65 tougher, with finer texture and of ahigher has incorporated with it cleavage products tensile strength thanthat obtained from ordil'ESllltlll" from the hydrolytic decompositionnary reclaimed rubber, especially where oil ofkeratln andwhichincorporation is brought is used as a softening or plasticizingagent. about by adding keratin to the rubber to be In the art ofreclaiming rubber it is essenreclaimed, and then subjecting both rubber"0 tial that. in addition to taking care of any andkcratin with it tothe devuleanizing procfree sulphur that may be present in the mass ifthe process of devulcanization be one and possibly a small portion ofthe combined embodying hydrolysis, of which the alkali sulphur, therubber scrap be softened or plasand heater processes of devulcanizationare 5 ticized to a point that will render it possible examples. In bothof these processes the T for the manufacturer to afterwards mix in scrapmaterial to be reclaimed is placed in various pigments or a percentageof crude heaters or digesters and subjected to a hyrubber, or bothpigments and rubber. In drolyzing action. In other words, the effectorder to do this it is essential that the reclaim is to obtain reclaimedrubber resulting from possess certain characteristics. In the first theaction of the hydrolyzed decomposition-so place it must be plasticenough to work readproducts of keratin upon the rubber scrap ily andstand a relatively high degree of heat during the process ofdevulcanization. without softening to a point that renders it As anexample of the process now practiced difficult to mill. on a warm mill.Ordinarily keratin preferably either finely divided in its themanufacturer adds a large quantity of natural state, or previouslyhydrolyzed, and S5 oil of various types to the variousgrades of inliquid or dry form. is intimately mixed reclaim in order to soften orplasticize them with the shredded scrap in the digester. If sufiicientlyfor working. purposes. The addi the reclaiming process is the customaryalkali ti on of a plasticizing oil however has its disreclaiming processthen keratin in its natural advantages. In the first place the rubberstate may be added to the mass. In case how- 9o worker has found inpractice that as soon ever the heater process be employed for deas areclaim carrying a high percentage of vulcanization then hydrolyzedkeratin-either oil comes in contact with a heated mill it bein dry orliquid form should be used. The comes so softened that it will notreadily mill relative amount of kerati n added to the rubber 4 and willat times become so soft that it sticks scrap will vary somewhat.dependent upon to the mill. This is aggravated by the fact the resultsdesired to be obtained. In practhat in those rubbers having a highcarbon tice preferably about 2% to 6% of keratin is 7 black content, asin the case of the modern added to the theoretical weight of rubbe intire tread. the oil content is increased in order the mass to betreated. "Ihe'mixture accoruto effect the necessary plasticizing action.A ing to the alkali process'of treatment 15 exposed to steam pressure,usually ranging from 100 to 200 pounds for periods of 12 to 24 hours,with the necessary additions of alkali and moisture dependent upon thekind of stock used. In the heater process the mixture is also exposed tosteam pressure for varying periods of time, dependent upon the stockemployed, with the addition of the necessary oil. In either case thematerial mixed with the scrap is subjected to a very drastic hydrolyzingaction while in the digester, the hydrolyzing action in theone casebeing carried forward by the action of caustic, heat, pressure, andmoisture, and in the other case by heat, pressure, and moisture. Thematerial used is accordingly completely broken down and in either case aproportion of the cleavage products of keratin present is utilized bythe rubber scrap after washing, to remove all the soluble material, withthe eficct of softening or plasticizing it to beter advantage than oil,and with the added advantage that when revulcanized the material isfirmer in texture with a higher tensile and finer grain than fromordinary reclaimed rubber and will not soften under service when incontact with heated surfaces. It is found also in practice that areclaimed rubber that has been plasticized with. these hydrolyticdecomposition products will disperse pigment in a shorter time thanordinary reclaim that has been plasticized by the use of oil. Thefinished prod not will not soften under service when exposed to theaction of a heated roadway or pavement but will maintain its elasticityand hardness and prevent excessive wear.

YVhen the hydrolyzed keratin is used in place of keratin in its naturalstate I prefer that there be used the cleavage products obtained by thehydrolytic decomposition of keratin as referred to in my Letters PatentNo. 1,683,863 of September 11, 1928.

The present reclaimed rubber which has been acted upon by the cleavageproducts of V keratin by which it is rendered more nine-- nable toprocessing before revulcanization, will possess a tter revulcanizationsome of the advantages possessed by the rubber composition referred toin my aforesaid patent and the full advantages thereof may be obtainedif the present reclaimed rubber, with or without fresh rubber added toit, have compounded therewith as a simple mix cleavage products of.keratin as referred to in my aforesaid patent.

Ha lng thus fully described my invention, I claim and desire to secureby Letter Patent of the United States:

1. Reclaimed rubber obtained from rubber scrap by a dcvulcanizingprocess having a hydrolytic action, in which the rubber scrap from whichthe reclaimed rubber is obtained has been subjected to the action ofcleavage products obtained from keratin during the CHARLES H.- CAMPBELL.

